Method and apparatus for casting metal articles with counter-gravity supply of metal to moulds

ABSTRACT

When casting metal articles in a mould by forcing molten metal upwardly through a filling tube by gas pressure in a closed chamber, the datum level just below that of a connector connecting the filling tube to the mould is registered by a level sensor in a sensing tube while the latter&#39;s upper end is connected to atmosphere through a vent tube. At the same moment, the pressure is measured by a pressure sensor and recorded by a control unit and maintained constant by the latter after the emptying of the sensing tube, by connecting its upper end to the chamber through an equalizing tube, until the pressure is increased to fill the mould according to a predetermined function of time programmed into the control unit. The starting point for the filling of all moulds in succession is the same, regardless of the amount of metal in the supply unit.

TECHNICAL FIELD

The present invention relates to an apparatus and a method of castingmetal articles in moulds having inlets at the side or bottom. Theapparatus comprises

a) a supply unit for molten metal comprising a closed chamber capable ofcontaining a mass of molten metal in its bottom region and a gas abovethe mass,

b) a filling tube extending from the bottom region upwardly to aconnector for temporary connection to a filling duct in a mould forcasting an article of metal,

c) means to vary the pressure in the gas between low values, at whichmetal from the mass when rising through the filling tube does not reachthe connector, and higher values, at which molten metal is made to flowthrough the connector into the filling conduit in the mould.

BACKGROUND ART

When previously carrying out a method of the kind referred to above,difficulties have been encountered when adjusting the level of metal inthe filling tube prior to the process of filling each mould with a viewto achieving identical starting points for the filling of all mouldsbeing filled successively. Previous attempts at determining the pressurecorresponding to the datum level of the molten metal in the filling tubejust prior to filling of each mould have not been very successful,because it has been based upon a computation of the difference in levelbetween the connector to be connected to each mould and the level of themass of metal contained in the supply unit. This computation is notparticularly accurate, and is not made easier by the fact that thesurface of the mass and metal in the supply unit is lowered upon eachcasting operation, possibly also reduced due to the limiting walls notbeing vertical or parallel.

From WO-A-89/07879 a die casting process of this kind is known. A sealedvessel with molten metal is via a filling tube temporarily connected toa mould and the molten metal is filled into the mould by a rising gaspressure in the vessel. A level indicator is provided in the fillingtube to ensure equal starting level of the melt for each new mould to befilled.

DISCLOSURE OF THE INVENTION

It is the object of the present invention to provide an apparatus and amethod of the kind referred to above, with which it is possible toensure that each single process of casting in each of the successivemoulds proceeds from the same starting point represented by the datumlevel referred to above, and this object is achieved by, according tothe invention, proceeding in the manner set forth in detail hereinbelow.By so doing, the datum level is determined for each and every mould,independently of the level of metal in the reservoir in the supply unit.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed part of the present description, the inventionwill be explained in more detail with reference to the exemplaryembodiment of an apparatus according to the invention shown in thedrawings, in which

FIGS. 1-4 are diagrammatic views in cross-section, showing the apparatusin various stages of carrying out the method.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus shown on the drawing comprises a supply unit 15 intendedto be substantially stationary in a pouring station of a moulding andcasting plant, such as one constructed upon the well-known DISAMATIC®principle. The supply unit 15 is adapted to supply molten metal from amass 10 of molten metal resting in the bottom region of a closed chamber16 within the supply unit by, through the use of gas pressure suppliedfrom a gas-supply unit 19 through a gas-supply conduit 4, forcing moltenmetal from the mass 10 upwardly through a filling tube 5 to a connector8 adapted for temporary connection to the filling conduit or runner 12in a mould 7, in which an article is to be cast. Branched from the upperend of the filling tube 5 is also, optionally, an external riser 9 thatcan be used to influence the filling of the mould 7. This far, onlypreviously known features of such apparatus have been described.

The main novel feature of the invention is the arrangement forcontrolling the initiation of the casting operation by sensing thepressure in the closed chamber 16. This arrangement comprises a sensingtube 2 extending from a location close to the bottom of the closedchamber 16 to outside of this chamber, terminating in a three-way valve11 with two positions. To this valve are also connected apressure-equalization tube 1 and a vent tube 3, the valve 11 being soarranged that it either, in the manner shown in FIGS. 1 and 2, connectsthe sensing tube 2 to the vent tube 3, and a position, in which itconnects the sensing tube 2 to the pressure-equalization tube 1 in themanner shown in FIGS. 3 and 4.

Further equipment includes

a level sensor 6 placed in the sensing tube at such a level that whenthe level of molten metal in the sensing tube rises to a level the sameas or just below the level of the connector 8, the sensor 6 reacts andsends a signal to

a control unit 14 adapted to control the operation of the apparatusincluding the gas-supply unit 19, possibly also of other parts (notshown) of the plant in response to i.a. signals from the level sensor 6and from

a pressure sensor 13 adapted to measure the pressure in the closedchamber 16.

The operation of the apparatus will now be described as a sequence ofevents shown in FIGS. 1-4.

In FIG. 1, the three-way valve 11 is in its first position, in which itconnects the sensing tube 2 to the vent tube 3 and thus to atmosphere. Afresh mould 7 has just been placed with its runner 12 connected to theconnector 8. The level of the molten metal 10 is the same in the sensingtube 2 and in the filling tube 5, but higher than in the closed chamber16 due to a moderate gas pressure being applied through the gas-supplyconduit 4. With the valve 11 in the position shown in FIG. 1, gaspressure in the gas-supply conduit 4 is now increased, causing themolten metal to rise in the sensing tube 2 as well as in the fillingtube 5. As shown in FIG. 2, the rising metal column in the sensing tube2 activates the level sensor 6 to send a signal to the control unit 14,the latter at this instant recording the pressure in the closed chamber16 as sensed by the pressure sensor 13, making a note of this pressureas a datum pressure, at which the metal column in the sensing tube 2just touches the level sensor 6. A datum pressure corresponding to adatum level, at which the metal column in the sensing tube 2 justtouches the level sensor 6, having now been recorded by the control unit14, the next step shown in FIG. 3 can now be carried out.

In the situation shown in FIG. 3, the three-way valve 11 is in itssecond position, in which it connects the sensing tube 2 to thepressure-equalization tube 1, so that there is no longer any pressuredifferential to hold a column of metal up against the level sensor 6.The level of metal in the filling tube 5 is, however, the same as shownin FIG. 2, because the upper end of the filling tube 5 is stillconnected to atmosphere through the external riser 9. According to theinvention, the level of metal in the filling tube 5 is maintained atthis level by suitably controlling the gas-supply unit 19 to maintainthe pressure in the closed chamber 16 at the previously recorded datumvalue established in the step shown in FIG. 2 and described above.

It is important at this stage to note that the level of metal in thefilling tube 5 will be at the datum level 17, regardless of whether thesupply unit 15 contains a smaller or larger amount of molten metal 10.

In the step shown in FIG. 4, the pressure in the closed chamber 16 isincreased by supplying additional gas through the supply conduit 4, soas to force the molten metal in the filling tube 5 to flow upward,partly to and through the connector 8 into the mould 7 through thelatter's runner 12, partly up into the external riser 9 to a fillinglevel 18, that may or may not be monitored by a further level sensor(not shown) e.g. of the same kind as the level sensor 6.

The process of filling the mould 7 in this manner is controlled in apre-programmed manner by the control unit 14, and it should be notedthat the starting point of this process will always be the situationshown in FIG. 3, regardless of the quantity of molten metal in the mass10. This, again, means that the tilling process proceeds in a manneruninfluenced by the level of metal in the mass 10, and will thus besubstantially identical from one mould 7 to the next.

The actual function of time, according to which the filling of the mould7 takes place by gradually increasing the pressure in the closed chamber16 in the range above the datum pressure, does not form part of theinvention, and will, of course, be adapted to the particular conditionsfor each run of casting operations, such as the shape and size of thecasting cavity, the characteristics of the casting metal etc.

After preventing backflow of the molten metal in the mould 7, such as bymeans of a suitable closure member (not shown), the pressure in theclosed chamber 16 can be reduced down to a value corresponding to thesituation shown in FIG. 3 or further, after which the mould 7 can beremoved and replaced by a fresh mould. The process of reducing thepressure in the closed chamber 16 can follow a predetermined function oftime, e.g. by suitably controlling the pressure applied by thegas-supply unit 19, or by controlling a relief valve (not shown)connecting the closed chamber 16 to atmosphere.

After this, the steps shown in FIGS. 1-4 are repeated, and it shouldespecially be noted as mentioned above that the datum pressure in theclosed chamber 16 corresponding to the datum level 17 is measured foreach and every mould, thus ensuring equal starting points for allmoulds.

What is claimed is:
 1. Apparatus for casting articles of metal in mouldshaving inlets at the side or bottom, the apparatus comprising a) asupply unit for molten metal comprising a closed chamber containing amass of molten metal in a bottom region thereof and a gas above themass, b) a filling tube extending from the bottom region upwardly to aconnector for temporary connection to a filling duct in a mould forcasting an article of metal, c) pressure-varying means to vary thepressure in the gas between (i) low values, at which metal from the masswhen rising though the filling tube does not reach the connector, and(ii) higher values, at which molten metal is made to flow through theconnector into the filling duct in the mould, d) a sensing tube, thelower end of which extends into the mass, e) a level sensor placed inthe sensing tube which reacts when the level of metal in the sensingtube is slightly lower than that of the connector, f) automatic controlequipment to which the level sensor and the pressure-varying means areconnected for controlling the operation of the apparatus including thepressure-varying means, and g) a switchable connecting system whichalternately connects an upper end of the sensing tube to a space outsidethe closed chamber and to the gas above the mass in the closed chamber.2. A method of casting articles of metal in moulds having inlets at theside or bottom comprising the steps of: using a sensing conduit of verysmall cross-sectional area compared to a surface area of molten metal ina closed chamber with gas above the molten metal, the sensing conduitextending from a bottom region of the closed chamber to an outside ofthe closed chamber, increasing a pressure of the gas until the level ofthe molten metal in the sensing conduit reaches a datum level, uponwhich the pressure of the gas is maintained at this datum value,connecting a mould to a connector connected to a filling tube in theclosed chamber, increasing the pressure of the gas into a higher rangeabove the datum value, switching an upper end of the sensing conduitfrom the outside to the gas in the closed chamber as the pressure isincreased from the datum value to prevent backflow in the sensingconduit, when the mould has been filled with molten metal through theconnector, reducing the pressure to or below the datum value, anddisconnecting the mould from the connector.
 3. A method according toclaim 2: a) wherein the sensing conduit is a separate sensing tube whichincludes a level sensor set at the datum level and connected toautomatic control equipment for controlling the casting operation, b)further including the step of measuring the pressure of the gas in theclosed chamber with a pressure sensor connected to the automatic controlequipment, and c) further including the step of maintaining the pressureof the gas at the datum value measured when the level sensor reactsuntil the pressure of the gas is increased for filling the mouldconnected to the connector.